package notify

import (
	"bytes"
	"errors"
	"io"
	"strings"
	"testing"
)

func TestNewTransferSourceFromReaderSequentialRead(t *testing.T) {
	source, err := NewTransferSourceFromReader(strings.NewReader("abcdef"), 6)
	if err != nil {
		t.Fatalf("NewTransferSourceFromReader failed: %v", err)
	}

	buf := make([]byte, 2)
	n, err := source.ReadAt(buf, 2)
	if err != nil {
		t.Fatalf("ReadAt resume offset failed: %v", err)
	}
	if got := string(buf[:n]); got != "cd" {
		t.Fatalf("ReadAt got %q, want %q", got, "cd")
	}

	n, err = source.ReadAt(buf, 4)
	if n != 2 {
		t.Fatalf("ReadAt n = %d, want 2", n)
	}
	if err != nil && !errors.Is(err, io.EOF) {
		t.Fatalf("ReadAt err = %v, want nil/EOF", err)
	}
	if got := string(buf[:n]); got != "ef" {
		t.Fatalf("ReadAt tail got %q, want %q", got, "ef")
	}

	if _, err := source.ReadAt(buf, 1); !errors.Is(err, errTransferSequentialSourceOrderedRead) {
		t.Fatalf("backward ReadAt err = %v, want %v", err, errTransferSequentialSourceOrderedRead)
	}
}

func TestNewTransferSinkFromWriterSequentialWrite(t *testing.T) {
	var dst bytes.Buffer
	sink, err := NewTransferSinkFromWriter(&dst)
	if err != nil {
		t.Fatalf("NewTransferSinkFromWriter failed: %v", err)
	}

	n, err := sink.WriteAt([]byte("ab"), 0)
	if err != nil {
		t.Fatalf("first WriteAt failed: %v", err)
	}
	if n != 2 {
		t.Fatalf("first WriteAt n = %d, want 2", n)
	}

	n, err = sink.WriteAt([]byte("cd"), 2)
	if err != nil {
		t.Fatalf("second WriteAt failed: %v", err)
	}
	if n != 2 {
		t.Fatalf("second WriteAt n = %d, want 2", n)
	}
	if got := dst.String(); got != "abcd" {
		t.Fatalf("writer got %q, want %q", got, "abcd")
	}

	offsetProvider, ok := sink.(interface{ NextOffset() int64 })
	if !ok {
		t.Fatal("sink does not expose NextOffset")
	}
	if got := offsetProvider.NextOffset(); got != 4 {
		t.Fatalf("NextOffset = %d, want 4", got)
	}

	if _, err := sink.WriteAt([]byte("x"), 1); !errors.Is(err, errTransferSequentialSinkOrderedWrite) {
		t.Fatalf("out-of-order WriteAt err = %v, want %v", err, errTransferSequentialSinkOrderedWrite)
	}
}

func TestNewTransferReaderFromSource(t *testing.T) {
	reader, err := NewTransferReaderFromSource(newTransferBytesSource([]byte("abcdef")), 2)
	if err != nil {
		t.Fatalf("NewTransferReaderFromSource failed: %v", err)
	}
	data, err := io.ReadAll(reader)
	if err != nil {
		t.Fatalf("ReadAll failed: %v", err)
	}
	if got := string(data); got != "cdef" {
		t.Fatalf("ReadAll got %q, want %q", got, "cdef")
	}
}

func TestNewTransferWriterFromSink(t *testing.T) {
	sink := &transferMemorySink{}
	writer, err := NewTransferWriterFromSink(sink, 0)
	if err != nil {
		t.Fatalf("NewTransferWriterFromSink failed: %v", err)
	}
	n, err := writer.Write([]byte("abcdef"))
	if err != nil {
		t.Fatalf("Write failed: %v", err)
	}
	if n != 6 {
		t.Fatalf("Write n = %d, want 6", n)
	}
	if got := string(sink.Bytes()); got != "abcdef" {
		t.Fatalf("sink bytes = %q, want %q", got, "abcdef")
	}
}

func TestNormalizeTransferSendOptionsRejectsSequentialSourceUnsupportedModes(t *testing.T) {
	source, err := NewTransferSourceFromReader(strings.NewReader("abcdef"), 6)
	if err != nil {
		t.Fatalf("NewTransferSourceFromReader failed: %v", err)
	}
	_, err = normalizeTransferSendOptions(TransferSendOptions{
		Descriptor: TransferDescriptor{
			ID:   "seq-parallel",
			Size: 6,
		},
		Source:      source,
		Parallelism: 2,
	})
	if !errors.Is(err, errTransferSequentialSourceParallelism) {
		t.Fatalf("normalize parallel err = %v, want %v", err, errTransferSequentialSourceParallelism)
	}

	source, err = NewTransferSourceFromReader(strings.NewReader("abcdef"), 6)
	if err != nil {
		t.Fatalf("NewTransferSourceFromReader failed: %v", err)
	}
	_, err = normalizeTransferSendOptions(TransferSendOptions{
		Descriptor: TransferDescriptor{
			ID:   "seq-checksum",
			Size: 6,
		},
		Source:         source,
		VerifyChecksum: true,
	})
	if !errors.Is(err, errTransferSequentialSourceImplicitChecksum) {
		t.Fatalf("normalize checksum err = %v, want %v", err, errTransferSequentialSourceImplicitChecksum)
	}
}